A multi-appearance telephone or attendant console equipped with a verify button is required.

You can use Busy Verification of Terminals and Trunks at a telephone or attendant console to make test calls to trunks, telephones, and hunt groups (DDC/UCD). These test calls check the status of an apparently busy resource. This provides an easy method to distinguish between a telephone or resource that is truly busy and one that only appears busy because of a trouble condition.